Discussion on the Reason Caused Low Yield Strength of X80 Pipeline Steel

In this article,it conducted system analysis on low yield strength occurred in initial production stage of X80 pipeline steel,by adopting Minitab statistical software,and carried out study from smelting compostition,steel rolling technology,metallographic structure and so on.The result showed that the process control ability of some key control points are high and don't appear abnormal,such as the the main strengthening elements C,Mn,Nb,Mo in melting components and the temperature of finish rolling and coiling.The main control point is that the high temperature of laminar flow cooling water lead to cooling rate decreasing,which directly result in abnormal metallographic structure,more quasi-polygonal ferrite and polygonal ferrite,uneven distribution of martensite and austenite islands,and nonuniform grain,finally,it generate low yield strength.